1. Field of the Invention
The present invention relates to an apparatus for displaying an image such as projectors and display devices, and a method for controlling a power supply.
2. Description of the Related Art
As a light source of a projector, a high-pressure mercury lamp is mainly used. It is necessary for the high-pressure mercury lamp to take a fixed period of time from the start of lighting to reach a stable state. Further, to extend the lamp's lifetime, the lamp has to be cooled down after use. A projector will not start to project an image until the lamp becomes stable even if a command to turn on a lamp's power supply is inputted, and the projector cools down the lamp for the fixed period of time after turning off the lamp's power supply when a command for turning off the lamp's power supply is inputted (see Japanese Patent Application Laid-Open No. 2007-47387). This is similarly applicable to another lamp used for the projector.
In either the time period from turning on the lamp's power supply until a stable lighting state of the lamp is reached, or in the time period from turning off the lamp's power supply until the lamp is cooled down, the projector will not accept a command from the user when the user activates the switch of the lamp's power supply.
A display device for a personal computer (hereinafter, referred to as “PC”) has a function in which a power supply is turned on when a video signal is inputted externally, and in which the power supply is turned off when the video signal supplied externally becomes absent. If this function is provided in a projector, a lamp's power supply can be automatically turned on and off, but the following problems may occur.
When the lamp's power supply is turned off because the video signal that has been inputted to the projector is absent, against the user's intention to keep it turned on, the lamp's power supply cannot be turned on until the lamp has cooled down even if the user wants to promptly turn on the lamp's power supply. The user has to wait until the projector is ready to accept a command by means of operating the lamp's on/off switch because the lamp cannot be immediately turned on again until it has cooled down. Further, when the lamp is again turned on, the user has to wait until the lamp reaches a stable state.